Stefania Martin
Charlotte Ibbotson*
Shreya Shah
Hennita Trivedy
Arfa Saleem
Introduction Cepaea nemoralis, commonly known as the grove snail, is an air-breathing land snail and is the subject of the study in this investigation. The land snail is very common in Europe and has a highly polymorphic shell pattern so very easy to locate and study. Its pattern can be distinguished relatively clearly from one another (unlike in other species) and C.nemoralisare a small species and thus easy to collect, which is one reason why these snails were the chosen species of study. The shell pattern (number of bands and colour) of this particular snail is simply inherited but the object is to assess whether genetic drift, gene flow and/or selection are the cause of differences (if there is any) in frequency levels. Snails tend to not move far in their lifetime (an estimation of 20m), and so selecting a study site large enough to carry out the investigation is far easier than say selecting humans, who travel a great deal more, to different continents! Due to their low lifespan, multiple generations can also be assessed. The sampling method involved a horizontal transect across two habitats, where six samples of snails were taken. A horizontal transect allows the control of altitude as a variable and thus it can be eliminated as a possible factor effecting the results. Woodland (the third type of habitat) was also eliminated purely due to lack of time, and as such only a limited number of samples could be taken. Removing woodland allowed replication of samples to occur in the other two habitats and thus a more detailed comparison could be taken and it increases the reliability of the results. Comparisons between (and within) each habitat could then be carried out. Another key point to the sample design is that the samples are far enough apart to ensure samples are independent reducing effects of gene flow. Control variables have been enforced to ensure independent samples were taken through large enough distances between samples. Another lesson is to ensure that variables that are not part of the analysis should be controlled. Repetition and replication must be present in the sampling method to allow comparisons to occur. Standardising the shell pattern categories of the C. nemoralis amongst the group before collection of data is also necessary to reduce human error. The null hypothesis states that selection does not play a part in the variation of the frequency, just genetic drift and gene flow. To support this hypothesis; inconsistent differences between the populations would be observed, supporting the fact that selection does not play a role as there isn’t one specific phenotype that is beneficial for a specific habitat. The alternate hypothesis states that genetic drift, gene flow and selection all play a role in the phenotypic variations between snail populations. To support this hypothesis, (to detect selection) consistent differences between each habitat sample would be observed.
Charlotte Ibbotson*
Shreya Shah
Hennita Trivedy
Arfa Saleem
Introduction
Cepaea nemoralis, commonly known as the grove snail, is an air-breathing land snail and is the subject of the study in this investigation. The land snail is very common in Europe and has a highly polymorphic shell pattern so very easy to locate and study. Its pattern can be distinguished relatively clearly from one another (unlike in other species) and C.nemoralis are a small species and thus easy to collect, which is one reason why these snails were the chosen species of study. The shell pattern (number of bands and colour) of this particular snail is simply inherited but the object is to assess whether genetic drift, gene flow and/or selection are the cause of differences (if there is any) in frequency levels. Snails tend to not move far in their lifetime (an estimation of 20m), and so selecting a study site large enough to carry out the investigation is far easier than say selecting humans, who travel a great deal more, to different continents! Due to their low lifespan, multiple generations can also be assessed.
The sampling method involved a horizontal transect across two habitats, where six samples of snails were taken. A horizontal transect allows the control of altitude as a variable and thus it can be eliminated as a possible factor effecting the results. Woodland (the third type of habitat) was also eliminated purely due to lack of time, and as such only a limited number of samples could be taken. Removing woodland allowed replication of samples to occur in the other two habitats and thus a more detailed comparison could be taken and it increases the reliability of the results. Comparisons between (and within) each habitat could then be carried out. Another key point to the sample design is that the samples are far enough apart to ensure samples are independent reducing effects of gene flow.
Control variables have been enforced to ensure independent samples were taken through large enough distances between samples. Another lesson is to ensure that variables that are not part of the analysis should be controlled. Repetition and replication must be present in the sampling method to allow comparisons to occur. Standardising the shell pattern categories of the C. nemoralis amongst the group before collection of data is also necessary to reduce human error.
The null hypothesis states that selection does not play a part in the variation of the frequency, just genetic drift and gene flow. To support this hypothesis; inconsistent differences between the populations would be observed, supporting the fact that selection does not play a role as there isn’t one specific phenotype that is beneficial for a specific habitat. The alternate hypothesis states that genetic drift, gene flow and selection all play a role in the phenotypic variations between snail populations. To support this hypothesis, (to detect selection) consistent differences between each habitat sample would be observed.